Bending arm causes odd deformation
might be caused because you have a low poly figure with (high?) subdivision.
The subdevision performs a smooth over the low poly figure.
creating artifacts.


copy your blend file, apply subdiv, then do another autoweights with bones.


Its always is a bit tricky but it might look better.
Sometimes people add extra bonus just to keep things stable, (ea rigify feed solution)..
placing of the bones is essential